Power semiconductor devices are semiconductor devices used for controlling electric equipment such as motors. With an increasing demand for energy saving and reduction in environmental loads in recent years, inverter control for motors has been developed and a demand for the power semiconductor devices has been increased rapidly along with development of markets for hybrid cars and electric cars.
In the power semiconductor device, a semiconductor chip for power control typically represented by IGBT (Insulated Gate Bipolar Transistor) or a rectifying diode chip is bonded by soldering over a metal circuit layer of a circuit substrate in which the metal circuit layer is formed over an insulating substrate. Then, a metal terminal such as made of copper (Cu) is bonded by means of ultrasonic metal bonding or a fine wire such as formed of aluminum (Al) or copper is bonded by wire bonding on one identical surface of the metal circuit layer where the chip and the solder are provided and connected directly or indirectly with a terminal of a casing of the power semiconductor device.
In the step of assembling such a power semiconductor device, if the processing temperature is excessively high, it causes a problem that not only the solder below the chip is melted and spreads from the inside to the outside of the chip failing to ensure sufficient thickness of the solder below the chip but also ultrasonic metal bonding or wire bonding can no more be attained if the solder spreads as far as the ultrasonic metal bonding portion or a wire bonding portion of the metal terminal.
The existent art for preventing the solder from flowing includes, for example, techniques disclosed in Japanese Unexamined Patent Application Publications Nos. 2004-71888 and Hei 08(1996)-31848. Japanese Unexamined Patent Application Publication No. 2004-71888 describes a semiconductor device in which grooves are formed over a circuit pattern by laser irradiation. Further, Japanese Unexamined Patent Application Publication No. Hei08(1996)-31848 describes a semiconductor device of heating the surface of a copper film selectively by a laser light thereby forming a copper oxide film.